<!DOCTYPE html>
<html lang="en-US">
<head>
<title>text-decoration alignment</title>
<meta charset=UTF-8>
<style>

span.block { position: absolute; top: 0; left: 0; }
span.dec { text-decoration: underline }
span.hide { color: transparent }

</style>
</head>
<body>

<p style="position: relative">
  <span class="block" style="margin-top: 16px"><span class="hide"></span><span class="dec" style="color:black  ">x<span class="hide">xx</span></span></span>
  <span class="block" style="margin-top: 08px"><span class="hide">x</span><span class="dec" style="color:fuchsia">x<span class="hide">x</span></span></span>
  <span class="block" style="margin-top: 00px"><span class="hide">xx</span><span class="dec" style="color:aqua   ">x<span class="hide"></span></span></span>
</p>

</body>
</html>
